....a quote from Ru-Fi-Oh in this thread.
http://forums.dlink.com/index.php?topic=6634.0
You don't need to forward anything for the 360 just as long as UPnP is checked in the router your should be good. Also check to see if SPI is turned off and NAT endpoint Independents is checked for both TCP and UDP, located in ADVANCED > FIREWALL SETTINGS